Recently, radio frequency (RF) and microwave power amplifiers have been used in the field of communication as they generate a relatively high amount of power that is useful in wireless communication systems. The RF and microwave power amplifiers are biased with various types of circuits. A well known type of circuit used for biasing is a current mirror circuit. In a typical current mirror circuit, a current source network is used to establish a reference current, provides up the current mirror. The current source network thus serves as a simple current regulator, supplying nearly constant current to a load over a wide range of load resistances.
In many RF and microwave power amplifiers, a resistor with a large value forms the current source network in the current mirror circuit. This approach is adequate in situations where the supply voltage is large. However, most battery operated circuits have a relatively low supply voltage, which renders the use of simple resistor biasing in the current mirror circuit inadequate. In order to overcome such limitations, alternative biasing methods are sometimes used, for example using a Gallium Arsenide Hetero-junction Bipolar Transistor (GaAs HBT) device to source the reference current from current source network. It will be seen that due to a relatively high value of base-emitter voltage in the device it may not be very reliable. In addition, the circuits using a GaAs HBT device tend to be very sensitive to changes in device behavior over long periods of high volume manufacturing.
In view of the foregoing, an improved current mirror circuit that is adaptive to supply voltage and ambient temperature variations, and tolerant to manufacturing variations is desirable.